code signing

'It's signed' means different things depending on when the signature is checked: once at install, every time the binary loads, or on every page of memory as it executes.

On a phone, the signing key is the app's identity: it decides who can ship updates, which data the app can share, and what it is entitled to do. Lose it, or let someone else sign, and that identity changes hands.

The mechanism takes a minute. The score comes from saying exactly what a valid signature does not prove, and running the key-theft response.

'Keyless' means no long-lived key, not no keys. The follow-up that separates candidates: what does your verification policy actually check?

Signed software outlives the certificate that signed it. The scored answer explains how a timestamp proves the signature was made while the certificate was valid, and how revocation dates interact with it.